Many hormone secretion and tissue responses to hormones that depend on cell membrane receptor transduction are blunted in old animals when compared to young animals. Such changes in hormonal responses are frequently due to alterations in the levels or ratios of stimulatory GTP-binding proteins (Gs) and inhibitory GTP binding proteins (Gi ) which mediate many membrane-bound receptor responses intracellularly. We have been conducting investigations of the effects of aging on the G-protein components of cyclase mediated catecholamines receptors in fat cell and hepatic cell membranes, and, more recently, have initiated studies of the effects of aging on responses of skeletal muscle and other tissues to GH and testosterone concentrating on EF-1alpha, a G protein which is a key mediator of protein synthesis at the ribosome. Activities in the past year have been devoted mainly to methods development and optimization of new assays for cyclase mediating G-protein complexes, for EF-1alpha mRNA to detect gene activation, and for EF-1alpha protein in tissue.